Regarding a reinforcement binding machine, JP 11-104777A and Japanese Utility Model Registration No. 2557192, filed by the applicant of the present application, disclose “Brake Mechanism of Wire Reel for Reinforcing Bar Binding Machine” and “Wire Reel for Binding Machine for binding Reinforcing Bar etc”, respectively.
FIGS. 38 and 39 show this reinforcement binding machine, in which a reel 2 around which a wire 3 is wound is retained at the rear of a reinforcement binding machine 1. The wire 3 drawn out of the reel 2 is fed to the front portion of the reinforcement binding machine 1 by a wire feeding means 5, and is curled as it is fed along a guide 6 having an arcuately extending groove to be formed into a loop around reinforcing bars 7 crossing each other in a cross-like form. The wire 3 wound around the reinforcing bars 7 in a loop-like form is grasped by a grasping portion 4, and then the wire feeding by the wire feeding means 5 stops; further, a twisting hook 8 having at its forward end a groove for holding the wire 3 in a loop-like form approaches the wire 3. After the wire is inserted into the groove, the twisting hook 8 rotates to thereby bind the reinforcing bars 7 with the wire 3. Then, the wire 3 is cut by a cutting means provided in the grasping portion 4, which then releases the wire 3.
In the rear portion of the reinforcement binding machine 1, there are provided a reel retaining portion (a cassette case (not shown)) for retaining the reel 2, an optical sensor arranged at a position on the reel retaining portion (cassette case) facing a side surface of the reel 2, and a mark arranged on the side surface of the reel 2 and detected by the optical sensor.
Further, in the rear portion of the reinforcement binding machine 1 shown in FIG. 39, there are provided an arm 9 for retaining the reel 2, an optical sensor arranged at a position on the arm 9 facing a side surface of the reel 2, and a mark arranged on the side surface of the reel 2 and detected by the optical sensor.
The optical sensor applies light to the side surface of the reel 2 and detects reflected light from the mark; when the reel 2 is rotating, reflected light is detected by the optical sensor substantially periodically.
When the wire 3 on the reel 2 has been consumed, the reel 2 does not rotate, so that no periodical reflected light from the mark is detected by the optical sensor, whereby it is determined that the wire 3 has been consumed. In FIG. 39, symbol A1 indicates a twisting mechanism, and symbol A2 indicates a trigger.
However, in the case of this reinforcement binding machine 1, when the optical sensor is exposed to the exterior, due to disturbance light intruding through the gap between the reel 2 and the reel retaining portion (cassette case) or between the reel 2 and the arm 9 shown in FIG. 39, the optical sensor may malfunction; further, when replacing the reel 2 whose wire 3 has been consumed or when detaching the reel 2, dust or dirt may adhere to the optical sensor to make it impossible to detect the mark on the reel 2, with the result that the optical sensor fails to detect the periodical reflected light, resulting in malfunctioning.
In Japanese Utility Model Registration No. 2557192 also, an optical sensor detection mark is similarly detected by an optical sensor. However, it has to be taken into account that the object to be detected (hereinafter, “detection object”) cannot be detected when the dimensions of the reinforcement binding machine 1 and the reel 2 or the way they are attached involve some play or when the detection object is stained or out of the proper distance range.